1. Field of the Invention
The present invention relates to the gain control of amplifiers, and more particularly, to gain control of variable gain amplifiers utilized in data detection circuits such as, for example, data detection circuits used with optical data disks.
2. Description of Related Art
In many data detection circuits an amplifier is used to boost an electrical signal received from a data storage media, such as a CD-ROM, DVD, or other optical disk, magnetic hard disk, etc. Data detection circuits may also be combined with circuitry for write operations. For example, circuitry for both read and write operations may be combined read/write channel circuits utilized with magnetic hard disks. In contrast, some optical disks are utilized in read only systems and thus the data detection circuit need not be combined with write circuitry.
In the case of optical disks, the electrical signal is generated from light that is reflected off an optical disk and converted to electrical pulses by an optical pickup head. The electrical pulses may then be transmitted to the front end of a variable gain amplifier prior for further signal processing. Typically the signal strength of the electrical pulses has many sources of variations including disks manufacturing inconsistencies, different optical pickup lens and photodiode configurations, and variations in the optical pickup head output power, etc. However, in order to obtain an optimal signal to noise ratio in the subsequent signal processing circuitry (circuitry such as, for example, an analog to digital converter) it is desirable to maintain a relative constant input signal level. Thus, it is desirable to utilize the variable gain amplifier in order to adjust the input signal level to an optimal signal level for subsequent data detection circuitry.
When implementing amplifiers in the data detection circuitry of optical storage systems, additional concerns exist. For example, the very high speed signals encountered with storage media require the amplifier to have a wide enough bandwidth to be able to process the data without attenuating the high frequency information. Thus, the gain control of the variable gain amplifier should be implemented without degrading the wideband nature of the amplifier.